Peristaltic pump having a motor overload protector

ABSTRACT

A peristaltic pump in which a tube is stably supported by a platen so as to be stably collapsed by fingers during normal operation, whereas, when an excessively large collapsing force is exerted by one of the fingers, the excess portion of the force is absorbed without fail so as to realize a stable pumping operation. The level or ability for absorbing the excess collapsing force is easily adjustable in accordance with changes in conditions such as the elasticity of the tube and the size of the tube. The tube can be stably set in a proper position between the platen and a group of the fingers.

This application is a continuation of application Ser. No. 07/558,051,filed Jul. 25, 1990, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a peristaltic pump suitable for use in,for example, transfusion.

2. Prior Art

Hitherto, various peristaltic pumps have been proposed as disclosed, forexample, in Japanese Unexamined Patent Publication No. 56-113084. Ingeneral, a known peristaltic pump has a plurality of cams, a pluralityof pressing fingers actuated by the cams so as to move between aretracted position and an operative position, and a platen opposing thepressing fingers so as to carry a tube therebetween. In operation, thepressing fingers are successively actuated to the operative position bythe cams so as to collapse the tube, whereby a liquid in the tube isdisplaced and transported, while the elastic tube is allowed to restorewhen relieved from the pressing force so as to expand the liquidpassage, thus performing a pumping action.

In the peristaltic pump of the type described, problems are caused suchas damaging of the tube due to excessive pressing, unduly large loadposed on the cam actuating device, and so forth, as a result of anydimensional errors caused during manufacture of the components such asthe cams, pressing fingers and the platen, as well as insufficiency inthe locating precision of these components. In order to obviate theseproblems, it has been proposed to provide an elastic support member onthe back side of the platen opposite to the pressing fingers, so thatany excessively large pressing force is absorbed by the elasticdeformation of the supporting member thereby relieving and unburdeningthe platen.

When the platen is unburdened, the pressing force to be relieved actsonly on a local point on the tube which is immediately under a certainpressing finger which has been set to the operative position. Therefore,during the unburdening, the platen does not always makes a translationalmovement. Namely, the platen may be moved at an inclination with respectto the plane of the group of pressing fingers. In such a case, thesupport of the tube on the platen is rendered unstable so as to impairthe precision in control of the flow rate of the liquid duringtransfusion.

Under this circumstance, Japanese Unexamined Utility Model PublicationNo. 62-20182 discloses a peristaltic pump which is improved to eliminatethe above-described problems concerning unburdening of the platen. Inthis improved peristaltic pump, any excessive force which would undulycollapse the tube is relieved not by a displacement of the platen but byelastic deformation of an elastic buffering portion of each pressingfinger made of an elastic material. Thus, any excessive force applied toa pressing finger, which would otherwise be exerted on the tube, iseffectively absorbed by the pressing finger itself.

PROBLEMS TO BE OVERCOME BY THE INVENTION

(A) This improved peristaltic pump disclosed in Japanese UnexaminedUtility Model Publication No. 62-20182, however, still suffers from thefollowing problems 1 and 2.

1 Since the pressing finger is made of an elastic material andincorporates an elastic buffer portion, the pressing surface of thepressing finger tends to be displaced by the elastic reaction forceproduced by the tube. It is therefore difficult to stably collapse thetube and, hence, to attain a stable pumping action.

2 Elastic buffer portions of different pressing fingers have differentlevels of absorption of excessive collapsing force and these levels areunadjustable. Therefore, when the elasticity or the size of the tube ischanged to require a different levels of force absorption, replacementof all the pressing fingers or the whole pump is inconvenientlyrequired.

Accordingly, an object of the present invention is to provide aperistaltic pump in which a tube is constantly and stably held by aplaten to allow the tube to be collapsed stably by pressing fingersunder normal operating condition and, in the event of an application ofany excessively large collapsing force, the excess of the collapsingforce is absorbed without fail, thus realizing a stable pumping action.

Another object of the present invention is to provide a peristaltic pumpwhich is improved to easily and freely adjust the level or ability toabsorb excessive collapsing force in accordance with a change in theelasticity of the tube, size of the tube and other factors.

(B) Another problem encountered with the known peristaltic pumpdisclosed in Japanese Unexamined Patent Publication No. 56-113084 is notdesigned to stably set the entire part of the tube at proper positionbetween the group of pressing fingers and the platen. This poses thefollowing problems 1 and 2.

1 The tube winds in the space between the pressing fingers and theplaten, so that the length of the portion of the tube pressed by eachpressing finger may differ from the design length.

2 The portion of the tube to be pressed by each pressing finger may bepartly placed out of the area where the pressing force by the pressingfinger is exerted.

These problems 1 and 2 make it immpossible to press successive sectionsof the tube of a predetermined length, thus impairing the precision ofthe flow rate control.

Accordingly an object of the present invention is to provide aperistaltic pump which enables a tube to be stably set at a properposition between a group of pressing fingers and a platen.

DISCLOSURE OF THE INVENTION

(A) To these ends, according to a first aspect of the present invention,there is provided a peristaltic pump comprising: a plurality ofeccentric cams; a cam shaft carrying the cams and capable of driving thecams; a plurality of fingers adapted to be driven by the cams so as topress and collapse a tube: a platen arranged to oppose the group offingers and capable of suppressing the movement of the tube in thedirection of the pressing; a movable member relatively movable towardand away from the platen and incorporating the cams, the cam shaft andthe pressing fingers; and urging means for urging the movable membertowards the platen; wherein, when an excessively large pressing force isexerted on the tube by one of the pressing fingers, the movable memberis moved away from the platen so as to reduce the pressing force exertedby the finger.

According to a second aspect of the present invention, there is provideda peristaltic pump of the first aspect, wherein the movable member isaccommodated in a housing while the platen is secured to a door which isprovided on the housing for movement between open and close positions.

According to a third aspect of the present invention, there is provideda peristaltic pump of the second aspect, wherein the urging meansincludes an urging member disposed between the movable member and thehousing, and an adjusting member capable of adjusting the urging forceof the urging member.

In the peristaltic pump of the first aspect of the invention,consecutive longitudinal sections of the elastic tube on the platen aresuccessively collapsed as the successive fingers of the finger group areactivated, namely, the position on the elastic tube where the collapsingforce is exerted is progressively moved in the longitudinal direction ofthe tube, so that the liquid in the tube is displaced, whereas theportion of the tube relieved from the collapsing fore is allows toresume its original force by its elasticity so as to expand the liquidpassage therein to suck a new portion of the liquid, whereby a pumpingaction is performed.

In the event that one of the pressing fingers is activated to exert anexcessively large collapsing force, a correspondingly large elasticreaction force produced by the tube forces the movable member away fromthe platen against the urging force produced by the urging means.Consequently, the finger incorporated in the movable member is movedtogether with the movable plate away from the platen, i.e., in thedirection opposite to the collapsing force exerted by the finger,whereby the excessive portion of the collapsing force exerted by thepressing finger is absorbed. In consequence, the tube is always stablyheld on the platen so that the tube is stably collapsed by thesuccessive fingers during normal operation, whereas, when anextraordinarily large collapsing force is generated by a finger, theexcessive portion of such a large collapsing force is absorbed withoutfail, whereby a stable pumping action is performed.

According to the second aspect of the invention, a compact constructionof the peristaltic pump of the first aspect can be realized by virtue ofthe fact that the cams, fingers and the platen are housed in the housingthrough the door. Furthermore, the tube can easily be mounted in aproper position between the fingers and the platen through the door.

According to a third aspect of the present invention, in the peristalticpump of the first or the second aspect, an adjusting member is providedfor enabling an adjustment of the urging force produced by the urgingmember which backs up the movable member against the elastic reactionforce produced by the tube. Thus, the level of force absorbed by adisplacement of the pressing finger together with the movable member inthe direction opposite to the collapsing force can easily be adjusted inaccordance with a change in conditions or factors such as the elasticityof the tube, size of the tube, and so forth.

(B) To these ends, according to a fourth aspect of the presentinvention, there is provided a peristaltic pump comprising: a pluralityof eccentric cams; a cam shaft carrying the cams and capable of drivingthe cams, a plurality of fingers adapted to be driven by the cams so asto press and collapse a tube; a platen arranged to oppose the group offingers and capable of holding the tube between itself and the fingers;and a tube holder disposed between the fingers and the tube and/orbetween the platen and the tube and having tube holding means which isprovided on the surface of the tube holder contactable with the tube andcapable of holding the tube in a predetermined position.

According to a fifth aspect of the present invention, there is provideda peristaltic pump of the fourth aspect, wherein the tube holderincludes a sheet-type elastic member having a recess-type tube holdingmeans formed in the surface thereof contactable with the tube.

According to a sixth aspect of the present invention, there is provideda peristaltic pump of the fifth aspect, wherein the tube holder includesat least a pair of tube clamping poritons projecting into the recess.

According to a seventh aspect of the present invention, there isprovided a peristaltic pump of the sixth aspect, further comprisingclamping fingers capable of pressing the clamping portions so as toenable the clamping portions to clamp the tube.

According to an eighth aspect of the present invention, there isprovided a peristaltic pump of the fourth, fifth, sixth, or seventhaspect, further comprising: a housing accommodating the cams, a camshaft and the fingers and supporting a tube holder such that the tubeholder is located at a position where it opposes the tube to be mounted;and a door supported on the housing for movement between open and closepositions and carrying the platen such that the platen opposes the tube.

According to a ninth aspect of the present invention, there is provideda peristaltic pump of the fourth, fifth, sixth, seventh, or eightaspect, wherein the surface of the tube holder to be contacted by thetube is made of a silicon rubber having a large coefficient of friction,while the surface of the tube holder to be contacted by the fingers ismade of a fluororesin having a small coefficient of friction.

According to a fourth aspect of the invention, consecutive longitudinalsections of the elastic tube on the platen are successively collapsed asthe successive fingers of the finger group are activated, namely, theposition on the elastic tube where the collapsing force is exerted isprogressively moved in the longitudinal direction of the tube, so thatthe liquid in the tube is displaced, whereas the portion of the tuberelieved from the collapsing fore is allows to resume its original forceby its elasticity so as to expand the liquid passage therein to suck anew portion of the liquid, whereby a pumping action is performed.

In this fourth aspect, as well as in a fifth aspect, of the presentinvention, a tube is properly placed without any winding, by means oftube holding means on the tube holder, such that successive tubesections of the design length are placed in the pressing regions of thesuccessive fingers, whereby the tube is correctly pressed by thesuccessive pressing fingers at the successive sections so as to providea high precision of control of the flow rate.

According to a sixth aspect of the present invention, the tube held bythe tube holding means in the pump of the fifth aspect is clamped by apair of clamp portions which are disposed at predetermined longitudinalposition of the recess-type holding means, so that the successivesections of the tube can be properly located within the regions of thesuccessive pressing fingers.

According to a seventh aspect of the present invention, the clampingportions of the tube holder in the sixth aspect of the invention arepressed by clamping fingers so that the locating precision of the tubeis further enhanced.

According to an eighth aspect of the present invention, the cams,pressing fingers, the platen and the tube holder in the fourth toseventh aspects are accommodated in the housing through the door,whereby a compact pump can be realized. Furthermore, the tube can be seton the tube holder and, hence, can be mounted very easily in the rightspace between the group of fingers and the platen when the door isopened and closed.

According to a ninth aspect of the present invention, the tube holder inthe fourth to eighth aspects of the present invention has a surfaceformed of a silicon rubber capable of stably holding the tube, while thesurface of the tube holder to be contacted by the pressing fingers isformed of a fluororesin having a small coefficient of friction, thusminimizing the wear of the portions of the tube holder to be contactedby the pressing fingers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the whole of a peristaltic pump;

FIG. 2 is a sectional view showing a critical portion of the peristalticpump of FIG. 1;

FIG. 3 is a longitudinal sectional view showing a critical portion ofthe peristaltic pump of FIG. 1;

FIG. 4 is an exploded perspective view showing critical portions of theperistaltic pump of FIG. 1;

FIG. 5 is a schematic illustration of operation of pressing fingers ofthe peristaltic pump;

FIG. 6 is a schematic illustration showing a guide plate and clampingfingers in the peristaltic pump;

FIG. 7 is a schematic illustration of operation of pressing fingers;

FIG. 8 is a schematic illustration of a guide plate and

FIG. 9 is a cross-sectional view of another embodiment of theperistaltic pump in accordance with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1 to 3, a peristaltic pump 10 has a housing 11 and adoor 13 connected to the housing 11 through a door shaft 12 forpivotally movement between an open position and a close position. Thedoor 13 is provided with a knob 14 which can be rotated to lock andunlock the door 13 in the close position.

The pump 10 is capable of effecting a pumping action on an intermediateportion of a tube 18 which is connected to a liquid guide needle 17piercing a stop cock 16 of a transfusion vessel 15 shown in FIG. 1, soas to transfuse a liquid from the transfusion vessel 15 into the body ofa patient. Numeral 19 denotes a ventilation needle.

As shown in FIGS. 2 to 4, the pump 10 has a movable member 22 rockablycarried by a pivot shaft 21 which is held at its both ends by brackets11A fixed to the housing 11. The pump 10 also has a platen 23 supportedon the door 13.

The movable member 22 is rockably supported by the pivot shaft 21 forrocking motion toward or away from the platen 23, and has a cam shaft 24which extends in parallel with the pivot shaft 21. The movable member 22also incorporates a plurality of eccentric cams 25 fixedly mounted onthe cam shaft 24 along the length thereof, and a plurality of fingers 26pivotally supported about the pivot shaft 21 and adapted to be pressedby the eccentric cams 25.

In this state, each finger 26 is adapted to be actuated by acorresponding eccentric cam 25 between a retracted position and anoperative position. When the door 13 is closed, the platen 23 can belocated so as to oppose the group 26A of fingers 26 so as to carry thetube 18 which is disposed between the platen 23 and the fingers 26. Thefingers are successively set to the operative position by the operationof the successive eccentric cams 25 so that the position where the tube18 is collapsed by the fingers is progressively moved in thelongitudinal direction of the tube. It is to be noted that the tube isnormally closed by at least one finger 26. The arrangement is such that,when one of the fingers 26 has commenced its backward movement beyondthe maximum collapse position, the next finger keeps the tube in pressedcondition so as to keep the internal liquid passage of the tube 18 untilthe above-mentioned finger 26 travels a distance large enough to openthe portion of the internal liquid passage under this finger 26.

The pump 10 also has an urging means 27 which resiliently urges themovable member 22 toward the platen 23. The urging means can be composedof a torsion spring 28 (urging member) and an adjusting screw (adjustingmember). In the illustrated embodiment, there are two torsion springs 28which are arranged on the pivot shaft 21 at the respective sides of themovable member 22. Each torsion spring has one end engaging with themovable member 22, while the other end engages with the end of anadjusting screw 29 which is screwed to each bracket 11A fixed to thehousing 11. In this state, the housing 11 carrying the brackets 11A towhich the adjusting screws 29 are screwed and the platen 23 supported bythe door 13 locked in the close position on the housing 11 are immovablerelative to each other. Consequently, the torsion springs 28 act betweenthe movable member 22 and the platen 23. The adjusting screws 29 can bedriven into and out of threaded holes formed in the brackets 11A so asto adjust the urging forces produced by the torsion springs 28.

The pump 10 also has a drive motor 31 fixed to the movable member 22 andhaving an output shaft carrying a worm gear 32 meshing with a worm wheel33 which is fixed to one end of the cam shaft 24.

The arrangement is such that the cam shaft 24 is rotatingly driven bythe drive motor 31 so as to rotate the eccentric cams 25 therebyactivating successive fingers 26, whereby a pumping action is performedas explained before.

The peristaltic pump 10 of the present invention has a tube guide deviceas will be understood from the following description.

Namely, as shown in FIG. 4, each bracket 11A on the housing 11 has apressing window 41 and a guide plate 42 for closing the pressing window41. The guide plate 42 is fastened to the bracket 11A by means of screws44 through a frame member 43 which presses the outer peripheral portionof the guide plate 42. As will be seen from FIGS. 2A and 2B, the guideplate 42 is provided with a tube guide groove 45 formed in the surfacethereof which faces the platen 23 when the door 13 is locked in theclose position on the housing 11 so as to set the tube 18. The guideplate 42 is made of a soft elastic material so as not to impede thecollapsing action of the fingers 26 when the successive fingers are setto the operative position for collapsing the tube 18. Therefore, asshown in FIG. 5A, the tube 18 is received in and guided by the guidegroove 45 of the guide plate 42 so as to be correctly set withoutwinding, in such a manner that successive tube sections of apredetermined length are correctly located in the pressing regions ofthe successive fingers. Consequently, the tube is stably collapsed bythe successive fingers as these fingers are set to the operativeposition, whereby a higher precision of control of the liquid flow ratecan be obtained, as will be seen from FIG. 5B.

As shown in FIG. 4, the guide plate 42 is provided with two pairs ofclamping portions 46 spaced in the longitudinal direction of the guidegroove 45 and formed onopposing walls of the guide groove 45 so as toproject into the guide groove 45 thereby to clamp the tube 18. The pairof clamping portions 46 of each pair oppose each other so as to definetherebetween a gap substantially equal to the outsidediameter of thetube 18. Thus, the clamping portions 46 serve to locate the tube 18 inthe groove 45 more precisely within the region where the collapsingforces are exerted by the successive fingers 26.

As shown in FIGS. 6 and 7, the peristaltic pump of the present inventionhas a plurality of clamping fingers 47 each of which are disposed atpositions corresponding to the respective pairs of opposing clampingportions 46 on the guide plate 42 and between two adjacent pressingfingers 26. Each clamping finger 47 is configured to have a recess whichsurrounds the portion of the guide plate 42 forming the guide recess 45,so as not to collapse the tube 18 and so as to press the clampingportions 46. As schematically shown in FIG. 7, each clamping finger 47is urged towards the clamping portions 46 by means of a backup spring 48acting between itself and the housing 11, thereby enhancing the locatingeffect of the clamping portions 46 for locating the tube 18.

The guide plate 42 is made of, for example, a rubber and the surface ofthe guide plate 42 opposite to the guide recess 45, i.e., the surface tobe pressed by the fingers 26, is embossed so as to reduce thecoefficient of friction, thereby suppressing friction due to contactwith the fingers 26.

As shown in FIG. 8, the guide plate 42 may be a composite member thesurface of which contactable with the tube 18 is formed from a materialhaving a large coefficient of friction, e.g., a silicon rubber 42A, soas to provide a stable support for the tube 18, while the surfacethereof to be pressed by the fingers 26 is formed from a material whichhas a small coefficient of friction and, hence, exhibits a smalltendency of wear, e.g., a fluororesin 42B.

The operation of the peristaltic pump having the described constructionis as follows:

1 The tube is set in the guide recess 45 formed in the guide plate 42and carried by the platen 23 so as to be located in the correct positionin the space between the group 26A of the pressing fingers 26 and theplaten 23. In this state, the pressing fingers 26 are activatedsuccessively by the operation of corresponding cams so as to be broughtinto their operative positions, so that the position of the collapsedportion of the tube is progressively moved in the longitudinal directionof the tube 18. Consequently, the liquid in the internal liquid passagein the tube is displaced so as to be delivered into, for example, thebody of a patient, while the portion of the tube relieved from thepressing force exerted by the pressing finger 26 resumes its originalform due to its elasticity so that the internal passage is expandedagain to suck a new portion of the liquid, whereby a pumping action isperformed.

When one of the fingers 26 of the group 26A is actuated to exert anextraordinarily large force onto the tube 18, a correspondingly largeelastic reaction fore produced by the tube serves to force the movablemember 22 backward away from the platen 23, against the force of theurging means 27, so that the finger 26 incorporated in this movablemember 22 is moved together with the movable member 22 away from theplaten 23, in.e., away from the tube 18, thereby absorbing excessportion of the collapsing force exerted by the finger 26. Consequently,the tube 18 is always held by the platen 23 in quite a stable manner andis smoothly collapsed by the successive fingers 26 under normaloperating condition. In the event that an extraordinarily large pressingforce is applied by one of the fingers 26, the excessive portion of thecollapsing force is absorbed without fail so as to protect the tube 18and to ensure a stable pumping operation.

In addition, the tube 18 is received in and guided by the tube guiderecess 45 formed in the guide plate 42 so that the entire portion of thetube is correctly set without wining, such that successive tube sectionsof a predetermined length are located in the successive areas wherepressing forces are to be applied by the successive pressing fingers 26.Therefore, the tube is collapsed in quite a stable manner as thesuccessive pressing fingers are set to operative positions, thusenhancing the precision in the control of the flow rate of the liquidunder transfusion.

2 The major and essential portions including the eccentric cams 25,pressing fingers 26 and the platen 23 which are housed in the housing 11by means of the door 13 so that a compact construction of the pump 10 isobtained. In addition, it is possible to set the tube 18 in the correctposition between the group 26A of the pressing fingers 26 and the tube18 very easily by the opening and closing action of the door 13.

3 The cam driving device of the pump is mounted on the movable member 22which incorporates the eccentric cams 25, so that the actuatingmechanism which operatively connects the eccentric cams 25 to the camdriving device can be set on the movable member 22, thus contributing toa simplification of the construction.

4 The urging force produced by the torsion spring 18, which backs up themovable member 22 against the elastic reaction force produced by thetube 18 is adjustable by means of the adjusting screw 29. Thus, theability of the pressing finger 26, which is displaceable together withthe movable member 22 to absorb any excessive collapsing force, isadjustable without difficulty in accordance with changes in conditionssuch as the elasticity of the tube 18, size of the tube 18 and so forth.

5 The pairs of clamping portions, which are provided at predeterminedpositions along the length of the guide recess 45 in the guide plate 42,effectively clamp the tube 18 so as to locate the tube 18 more preciselyin the region where the collapsing pressing forces are exerted by thesuccessive pressing fingers 26.

6 By pressing the clamping portions 46 on the guide plate 42 by means ofthe clamping fingers 47, it is possible to enhance the locating effectof the clamping portions 46 for locating the tube 18.

7 A compact construction of the pump 10 is obtained by virtue of the useof the housing 11 with the door 13 for accommodating the eccentric cams25, pressing fingers 26 and the platen 23. In addition, it is possibleto easily set the tube 18 in the guide plate 42 when the door is openedand closed, whereby the tube 18 can be correctly located in the spacebetween the group 26A of the pressing fingers 26 and the platen 23.

The guide plate 42 of the pump 10 serves to stably locate the tube 18 inthe region where the collapsing forces are applied by the successivepressing fingers so as to enhance the precision of control of the flowrate of the liquid, and covers the pressing window 41 in the bracket 11Aso as to prevent the liquid flowing in the tube 18 from accidentallycoming into the mechanical portion of the pump. Consequently,contamination of the mechanism also is prevented.

FIG. 9 shows a second embodiment of the peristaltic pump of the presentinvention. The peristaltic pump shown in FIG. 9 is different from theperistaltic pump of the first embodiment in that the fingers arearranged for linear movement with respect to the movable member, as willbe understood from the following description.

Referring to FIG. 9, the peristaltic pump 50 of the second embodimenthas, as is the case of the first embodiment, a housing 51, a door shaft52, a door 53 and a knob 54.

The pump 50 also has a support shaft 61 which is carried at its bothends by a bracket 51A fixed to the housing 51. The support shaft 61rockably carries a movable member 62. The pump 50 also has a platen 63supported by the door 53.

The movable member 62 is supported for rocking motion around the supportshaft 61 toward and away from the platen 63. The movable member 62 has acam shaft 64 which extends in parallel with the support shaft 61 andincorporates a plurality of cams 65 fixedly carried by the cam shaft 64and arranged along the length of the support shaft 61. The movablemember 62 also incorporates a plurality of pressing fingers 66 which areadapted to be linearly actuated by the cams 65.

Thus, each of the pressing fingers 66 is movable between a retractedposition and an operative position by the action of the associated cam65. The platen 63 is adapted to be positioned so as to oppose the group66A of fingers 66 so as to hold the tube 18 between itself and thepressing fingers 66. As the successive cams are operated, the associatedfingers are set to the operative positions so that the position of thecollapsed portion of the tube is progressively moved in the longitudinaldirection of the tube.

The pump 50 further has an urging means 67 which urges the movablemember 62 towards the platen 63. The urging means 67 is composed of atensile spring 68 (urging member) and an adjusting screw 69 (adjustingmember). The tensile spring 68 has one end retained by an end of theadjusting screw 69 which is screwed to the movable member 62 and theother end which is retained by the bracket 51A on the housing 51. Theadjusting screw 69 can be driven into and out of the threaded hole inthe bracket 51A so as to adjust the urging force produced by the tensilespring 68.

The pump 50 also has a drive motor 71 mounted on the movable member 62and capable of driving the cam shaft 64 so as to rotate the cams 65 onthe camshaft 64, thereby operating the pressing fingers 66 correspondingto these cams 65.

As in the case of the pump 10 of the first embodiment, the pump 50 has aguide plate 82 which is disposed to cover the pressing window 81 in thebracket 51A of the housing 51 and which is provided with a tube guiderecess 83 for setting the tube 18. Numeral 84 denotes a frame.

The pump 50 having the described construction operates substantially inthe same manner as the pump 10 of the first embodiment.

In the first embodiment as described, the movable member is supportedfor linear motion with respect to the housing.

EFFECT OF THE INVENTION

As has been described, according to the first to third aspects of thepresent invention, the tube is always held in a stable manner by theplaten and is stably collapsed by the successive fingers under normaloperating condition, whereas, in the event that an extraordinarily largeforce is applied, the excess portion of the collapsing force exerted bythe pressing finger is effectively absorbed so as to ensure a stablepumping operation.

Furthermore, according to the first to third aspects of the invention,it is possible to easily adjust the level of the excess collapsing forceto be absorbed, in accordance with a change in the conditions such asthe elasticity of the tube, size of the tube, and so forth.

In addition, according to the fourth to ninth aspects of the invention,it is possible to stably set the tube in the right position between thegroup of pressing fingers and the platen.

What is claimed is:
 1. A peristaltic pump comprising:a motor means; a plurality of eccentric cams; a cam shaft connected to be driven by said motor means for carrying and driving said plurality of eccentric cams; a plurality of fingers pivotally positioned along an axis of a pivot shaft, said plurality of fingers being pivotal about said axis of said pivot shaft and being adapted to be successively driven by said plurality of eccentric cams to pivot about said pivot shaft for pressing and collapsing a flexible tube in a given direction along said axis; a platen arranged to oppose said plurality of fingers for suppressing a movement of said flexible tube in the given direction; said plurality of fingers being urged to press said flexible tube by said plurality of eccentric cams and said cam shaft, said plurality of fingers respectively being pivotally mounted for pivotal movement toward and away from said platen; and urging means positioned coaxially with said axle of said pivot shaft for urging said plurality of fingers toward said platen up to a predetermined position.
 2. A peristaltic pump as set forth in claim 1, wherein said urging means comprises an adjusting member for preventing said urging means from providing an excessive urging force on said flexible tube by said plurality of fingers.
 3. A peristaltic pump as set forth in claim 1, further comprising a guide member for stably positioning said flexible tube within a pressing region. 